Developer for electrostatic images



Patented Nov. 18, r 1952 11 DEVELQPER FOR ELECTROSTATIC IMAGES Lewis E.Walkup, Columbus, Ohio, assignor, by mesne assignments, to The HaloidCompany,

Rochester, -N. Y., a corporation of New York No Drawing. ApplicationOctober 20, I948, Serial No. 55,645

13 Claims.

This invention relates to a developer for electrostatic images, withparticular reference to the development of electrostatic images onplates such as used in electrophotographic processes where a sensitivelayer .is charged electrostatically and then exposed to receive allatentelectrostatic image which is developed by a developer that results in apowder image, the powder image .being then transferred to asheet oftransfer material, and the invention has .for its purpose to afford adeveloper composed of electroscopic powder and a granular carrier.material that is more efiicient and not open to the objectionablecharacteristics that have been present in developers heretofore employedfor this purpose, also which enables a reduction in the cost of thegranular carrier material and makes possible carriers having magneticproperties,

The developers previously used comprise in general a mixture of asuitable pigmented or dyed electroscopic powderand a granular carriermaterial, which latter functions to carry and to generate triboelectriccharges on the electroscopic powders as well as to remove excess powder.from uncharged or slightly charged or background areas of the plate,and it has been found that in some instances, the granular carriermaterial exhibits a tendency to adhere to the image bearing plate, thuspreventing the proper functioning of the electroscopic powder andblocking theimage more or less, and it is ,a particular purpose of theinvention to so form the granular carrier material that it is not likelyto adhere to the charged or uncharged areas of the plate, and

to insure the removal of substantially all of the granular carriermaterial from the plate, leaving only the electroscopic powder particleswhich are attracted and retained by the charged areas.

Another purpose of the invention is to enable controlling the specificgravity of the granular carrier material in relation to theelectroscopic developing powder whereby any desired relation between thespecific .gravities oi the two components of the mixture may be hadwhile maintaining a proper triboelectric charging relationshipbetween-them.

In general, the'invention comprises the utilization of a granularcarrier material consisting of a core, base or interior composed of anyselected material which may be of high specific gravity such as glass orsteel beads, covered with and encased in a suitable covering whichimparts the necessary tri'boelectric properties to the granular carriermaterial, so that it will properly charge the electroscopic powder whenmixed therewith,

while maintaining such a relative specific gravity as to insure againstadherence of the granular carrier material to the charged plate.

Such a high specific gravity granular carrier material may be producedby adhering anouter covering consisting of a selectedtriboelectric'resinous or other suitable substance to the core-or baseparticles of glass or steel beads or the like by first coating the coreparticles with an intermediate bonding layer, for example a liquid resinwhich contains a hydrochloric acid catalyst. The coated core or base"particles are then added to the dry triboelectri'c resinoussubstancewhich adheres thereto and constitutes a covering that is fused orotherwise affixed to the core'or base particles, any remaining finesbeing separated by screening, and such coated granular carrier materialis then mixed with the 'electroscopic powder to form the-developer.

The invention is carried out by employing an electroscopic powder suchas a mixture of 20 parts Amberol F-7l, a phenol-formaldehyde resinmanufactured by Resinous Products & Chemical Co., 222 West WashingtonSquare, Philadelphia-5, Pa, and 1 part carbon black such as Raven BeadCarbon Black manufactured by Binney & Smith Co., 41 East 42nd Street,New York 7, N. Y. The electroscopic powder is prepared by mixing theabove ingredients and breaking them to a 16- mesh size or smaller, afterwhich approximately 225 grams of the mixture are placed in a onehalfgallon capacity ball mill 'jar containing an aluminum scraper. The jaris filled to approximately three-quarters :its capacity with diamterballs and the mixture ball milled for about four hours, after which it'is removed from the ball mill jar and iused'on a hot plate undersuitable heating lamps or by other suitable means. The mixture is thencooled and broken into approximately Iii-mesh size particles, followingwhich it is micropulverized to an average size of from 1 to 20 micronssubstantially as disclosed in copending application Ser. No. 24,674,filed May 1, 1948.

It has been ascertained-that in order to develop a latent imagecomprised of negative electrostatic charges, an electroscopic powder andgranular carrier combination should be selected in which the powder istriboelectrically positive to the granular carrier, and to develop alatent image comprised of positive electrostatic charges, anelectroscopic powder and granular carrier should beselected in whichthepowder is tr-iboelectrically negative to the granular carrier.

This triboelectric relationship between the powder and granular carrierdepends on their relative positions in a triboelectric series in whichthe materials are arranged in such a way that each material is chargedwith positive electricity When contacted with any material below it inthe series and with negative electricity when contacted with anymaterial above it in the series. In the reproduction of high contrastcopy such as letters, tracings, etc., it is desirable to select theelectroscopic powder and granular carrier materials so that their mutualelectrification is considerable, and the degree of such electrificationis governed in most cases by the distance between their positions in thetriboelectric series, that is, the greater distance they are removedfrom one another, the greater the mutual electrification, and the closerthey are together in Example 1 A suitable granular carrier material foruse with plates carrying a negative electrostatic charge is made byusing 200 parts glass beads and a covering consisting of 40 partsVinylite VYLF (a vinyl chloride-vinyl acetate copolymer produced byBakelite Corporation, 30 East 42nd Street, New York, N. Y.), 8 partsDurite X221 (a phenol-furfural and phenol-formaldehyde thermosettingresin and molding compound manufactured by The Borden Company, ChemicalDivision, Philadelphia, Pa), and 8 parts Durez 12763 (aphenol-formaldehyde molding compound and resin material manufactured byDurez Plastics llz Chemical Inc., North Tonawanda, N. Y.), said coveringbeing bonded to the glass bead base or core particles by a resinadhesive intermediate coating consisting of 16 parts Durez 8286 (aphenol-formaldehyde molding compound and resin manufactured by DurezPlastics & Chemical Inc., North Tonawanda, N. Y.) catalyzed with 1.5 cc.of a 50% hydrochloric acid. The core particles are first coated with theliquid bonding resin containing the catalyst, and then mixed with thedry covering material, which adheres to the bonding resin on the coreparticles, andis then fused thereto in any suitable manner. anyremaining fines being removed by screening.

The final granular carrier particles are preferably smaller than30-mesh, i. e. an outer diameter of approximately 0.023 inches, andlarger than 50-mesh, i. e. an outer diameter of approximately 0.012inches, in size, and the electroscopic powder is preferably mixed withthe granular carrier material in the proportion of 6 to 170.

Example 2 Another granular carrier material suitable for use withnegatively charged plates consists of 200 parts of glass bead coreparticles covered with 40 parts Saran B115 (a vinylidene chloride resinmanufactured by Dow Chemical Co., Midland, Mich.), 16 parts Durite X221,and 16 parts Durez 12763, the covering being adhered to the glass beadcore or base particles by a resin bonding agent consisting of 16 partsBakelite BR7534 (a resin material manufactured by Bakelite Cor- 4poration, 30 East 42nd Street, New York, N. Y.) to which has been addeda catalyst consisting of 1.5 cc. of a 50% hydrochloric acid. Thisgranular carrier material is produced in the same manner as alreadydescribed, by first applying the liquid bonding resin and catalyst tothe core particles, and then adding the core particles coated with thebonding resin to the dry covering material, which imparts the necessarytriboelectric properties to the core particles.

This granular carrier material when in its final form is preferably of asize smaller than 30-mesh and larger than 50-mesh, and the electroscopicpowder is preferably mixed With(. such granular carrier material in theproportion of 10 to 240.

Example 3 Another ranular carrier material suitable for use withnegatively charged plates is produced in a similar manner by using 200parts of glass beads for the base or core particles, which are coveredwith 40 parts Pliolite (a butadiene polymer manufactured by GoodyearTire & Rubber Co., Akron, Ohio), 8 parts Durez 12763, and 8 parts DuriteX221, the covering being adhered to the base or core particles by aresin bonding agent consisting of 16 parts Bakelite BR7534 to which hasbeen added a catalyst consisting of 2 cc. of a 50% hydrochloric acid.

The size of the final granular carrier particles are the same as statedabove in connection with Examples #1 and #2, and the electroscopicpowder is preferably mixed with such granular carrier material in theproportion of 6 to 225.

Example 4 A suitable granular carrier material for use with a positivelycharged plate is made by using 500 parts of steel beads for the base orcore particles, which are covered with 60 parts Melmac 401 (athermosetting, melamine-type synthetic resin manufactured by AmericanCyanamid Co., Plastics Division, New York 20, N. Y.), 40 parts VinyliteVYNS, and 5 parts Nigrosine Base 10 (a black dye manufactured by theCalco Chemical Division of the American Cyanamid Company, Boundbrook, N.J.) adhered to the core or base particles by a bonding agent consistingof 15 parts Bakelite BR7534, to which has been added a catalystconsisting of 1 cc. of a 50% hydrochloric acid.

The granular carrier particles are the same size as stated above, andthe electroscopic powder is preferably mixed with such granular carriermaterial in the proportion of 8 to 300.

Example 5 Another granular carrier material suitable for use withpositively charged plates is produced by applying the same covering asspecified in the last mentioned Example #4 to a base or core particlesconsisting of parts of glass beads, and adhering th covering to the coreparticles by a bonding agent consisting of 16 parts Bakelite BR7534 towhich has been added a catalyst consisting of 1.5 cc. of a 50%hydrochloric acid.

The granular carrier particles are the same size as stated above, andthe electroscopic powder is preferably mixed with such granular carriermaterial in the proportion of 10 to 230.

Example 6 Another satisfactory granular carrier material for use with apositively charged plate is produced by using carborundum for the baseor core particles, covering the same with 60 parts Melmac 4'01, 40 partsVinylite VYNS, and 5 parts Nigrosine Base 10, adhered to the core orbase particles by a bonding agent consisting of parts Bakelite BR7534 toWhich has been added a catalyst consisting of 1 cc. of a 50%hydrochloric acid.

This granular carrier material is preferably of a size smaller than-mesh and larger than SO-mesh, and the electroscopic powder ispreferably mixed with such granular carrier material in the proportionof 8 to 300.

Example 7 Another satisfactory granular carrier material for use inprinting from a plate carrying a negative charge is made by using 200parts of glass beads for the core or base particles, covering the samewith parts Pliolite, 8 parts Durez 12763, and 8 parts Durite X221,adhered to the base particles by a bonding agent consisting of 15 partsBakelite Eli/753 i to which has been added a catalyst consisting of 2cc. of a hydrochloric acid.

The size of the granular carrier material is the same as stated in theprecedin examples, and the electroscopic powder is preferably mixed withsuch granular carrier material in the proportion of 6 to 225.

While the invention has been described in connection with certainspecific materials, it is not confined to the details herein disclosed,and this application is intended to cover such modifications ordepartures as may come within the purposes of the improvements or thescope of the following claims.

I claim:

1. A developer for electrostatic latent images comprising a dry mixtureof loose movable particles of electrostatically-attractable powder andseparate granular carrier material, the granular material being composedof loose, freely movable particles each of which includes a core havinga specific gravity higher than the specific gravity of the powderparticles, whereby it does not adhere to electrostatic latent imagesurfaces, and a coating permanently bonded on said core, said coatingand powder particles having a triboelectric relationship of oppositepolarity, the powder particles thereby bein electrostatically chargedthrough triboelectric action by mixing with the granular carriermaterial to movably adhere electrostatically to the surface of thecarrier granules and being attractable by an electrostaticallychargedinsulating layer, and the coating of the granular material beingcorrespondingly electrostatically charged to opposite polarity and thusadapted to attract said charged powder particles and to remove them fromuncharged areas of the electrostatic latent image surface when cascadedthereacross.

2. A developer for electrostatic latent images comprising a dry mixtureof loose movable particles of electrostatically-attractable powder andseparate granular carrier material, the granular material being composedof loose, freely movable particles each of which includes a core havinga specific gravity higher than the specific gravity of the powderparticles, whereby it does not adhere to electrostatic latent imagesurfaces, and a resin coating permanently bonded on said core, saidcoating and powder particles having a triboelectric relationship ofopposite polarity, the powder particles thereby being electrostaticallycharged through triboelectric action by mixing with the granular carriermaterial to movably 6 adhere electrostatically to the surface of thecarrier granules and being attractable by an electrostatically-chargedinsulating layer, and the coatin of the granular material beingcorrespondingly electrostatically charged to opposite polarity and thusadapted to attract said charged powder particles and to remove them fromuncharged areas of the electrostatic latent image surface when cascadedthereacross.

3. A developer for electrostatic latent images comprising a dry mixtureof loose movable particles of electrostatically-attractable powder andseparate granular carrier material, the granular material being composedof loose, freely movable particles each of which includes a core havinga specific gravity higher than the specificgravity of the powderparticles, whereby it does not adhere to electrostatic latent imagesurfaces, a resin coating permanently bonded on said core and anintermediate adhesive coat bonding said coating to the core, saidcoating and powder particles havin a triboelectric relationship ofopposite polarity, the powder particles thereby being elec trostaticallycharged through triboelectric action by mixing with the granular carriermaterial to m-ovably adhere electrostatically to the surface of thecarrier granules and being attractable by an electrostatically-chargedinsulating layer, and the coating of the granular material beingcorrespondingly electrostatically charged to opposite polarity and thusadapted to attract said charged powder particles and to remove them fromuncharged areas of the electrostatic latent image surface when cascadedthereacross.

4. A developer for electrostatic latent images comprising a dry mixtureof loose movable particles of electrostatically-attractable powder andseparate granular carrier material, the granular material being composedof loose, freely movable particles each of which includes a glass beadcore having a specific gravity higher than the specific gravity of thepowder particles, whereby it does not adhere to electrostatic latentimage surfaces, a resin coating permanently bonded on said core and anintermediate adhesive coat bonding said coating to the core, saidcoating and powder particles having a triboelectric relationship ofopposite polarity, the powder particles thereby being electrostaticallycharged through triboelectric action by mixing with the granular carriermaterial to movably adhere electrostatically to the surface of thecarrier granules and being attractable by an electrostatically-chargedinsulating layer, and the coating of the granular material beingcorrespondingly electrostatically charged to opposite polarity and thusadapted to remove said charged powder particles from uncharged areas ofthe electrostatic latent image surface when cascaded thereacross.

5. A developer for electrostatic latent images comprising a dry mixtureof loose movable particles of electrostatically-attractable powder andseparate granular carrier material, the granular material being composedof loose, freely movable particles each of which includes a carborundumcore having a specific gravity higher than the specific gravity of thepowder particles, whereby it does not adhere to electrostatic latentimage surfaces, a resin coating permanently bonded on said core and anintermediate adhesive coat bonding said coating to the core, saidcoating and powder particles having a triboelectric relationship ofopposite polarity, the powder particles thereby being electrostaticallycharged through triboelectric action by mixing with the granular carriermaterial to movably adhere electrostatically to the surface of thecarrier granules and being attractable by an electrostatically-chargedinsulating layer, and the coating of the granular material beingcorrespondingly electrostatically charged to opposite polarity and thusadapted to remove said charged powder particles from uncharged areas ofthe el ctrostatic latent image surface when cascaded thereacross.

. 6. A developer for electrostatic latent images comprising a drymixture of loose movable particles of electrostatically-attractablepowder and separate granular carrier material, the granular materialbeing composed of loose, freely movable particles each of which includesa steel bead core having a specific gravity higher than the specificgravity of the powder particles, whereby it does not adhere toelectrostatic latent image surfaces, a resin coating permanently bondedon said core and an intermediate adhesive coat bonding said coating tothe core, said coating and powder particles having a triboelectricrelationship of opposite polarity, the powder particles thereby beingelectrostatically charged through triboelectric action by mixing withthe granular carrier material to movably adhere electrostatically to thesurface of the carrier granules and being attractable by anelectrostaticallycharged insulating layer, and the coating of thegranular material being correspondingly electrostatically charged toopposite polarity and thus adapted to remove said charged powderparticles from uncharged areas of the electrostatic latent image surfacewhen cascaded thereacross.

7. In an electrographic process wherein an electrostatic latent image isdeveloped to yield an electrostatically adhering image ofelectrostatically attractable material, the improvement comprisingdeveloping the ima e by cascading thereacross a dry mixture of loosemovable particles of electrostatically-attractable powder and separategranular carrier material, the granular material being composed ofloose, freely movable particles each of which includes a core having aspecific gravity higher than the specific gravity of the powderparticles, whereby it does not adhere to electrostatic latent imagesurfaces, and a coating permanently bonded on said core, said coatingand powder particles having a triboelectric relationship of oppositepolarity, the powder particles thereby being electrostatically chargedthrough triboelectric action by mixing with the granular carriermaterial to movably adhere electrostatically to the surface of thecarrier granules and being attractable by an electrostatically-chargedinsulating layer, and the coating of the granular material beingcorrespondingly electrostatically charged to opposite polarity and thusadapted to attract said charged powder particles and to remove them fromuncharged areas of the electrostatic latent image surface when cascadedthereacross.

8. In an electrographic process wherein an electrostatic latent image isdeveloped to yield an electrostatically adhering image ofelectrostatically attractable material, the improvement comprisingdeveloping the image by cascading thereacross a dry mixture of loosemovable particles of electrostaticallyattractable powder and separategranular carrier material, the granular material being composed ofloose, freely movable particles each of which includes a core having aspecific gravity higher than the specific gravity of the powderparticles, whereby it does not adhere to electrostatic latent imagesurfaces, and

a resin coating permanently bonded on said core, said coating and powderparticles having a tribeelectric relationship of opposite polarity, thepowder particles thereby being electrostatically charged throughtriboelectric action by mixing with the granular carrier material tomovably adhere electrostatically to the surface of the carrier granulesand being attractable by an electrostatically-charged insulating layer,and the coating of the granular material being correspondinglyelectrostatically charged to opposite polarity and thus adapted toattract said charged powder particles and to remove them from unchargedareas of the electrostatic latent image surface when cascadedthereacross.

9. In an electrographic process wherein an electrostatic latent image isdeveloped to yield an electrostatically adhering image ofelectrostatically attractable material, the improvement comprisingdeveloping the image by cascading thereacross a dry mixture of loosemovable particles of electrostatically-attractable powder and separategranular carrier material, the granular material being composed ofloose, freely movable particles each of which includes a glass bead corehaving a specific gravity higher than the specific gravity of the powderparticles, whereby it does not adhere to electrostatic latent imagesurfaces, and a resin coating permanently bonded on said core, saidcoating and powder particles having a triboelectric relationship ofopposite polarity, the powder particles thereby being electrostaticallycharged through triboelectric action by mixing with the granular carriermaterial to movably adhere electrostatically to the surface of thecarrier granules and being attractable by an electrostatically-chargedinsulating layer, and the coating of the granular material beingcorrespondingly electrostatically charged to opposite polarity and thusadapted to attract said charged powder particles and to remove them fromuncharged areas of the electrostatic latent image surface when cascadedthereacross.

10. In an electrographic process wherein an electrostatic latent imageis developed to yield an electrostatically adhering image ofelectrostatically-attractable material, the improvement comprisingdeveloping the image by cascading ther across a dry mixture of loosemovable particles of electrostatically-attractable powder and separategranular carrier material, the granular material being composed ofloose, freely movable particles each of which includes a steel bead corehaving a specific gravity higher than the specific gravity of the powderparticles, whereby it does not adhere to electrostatic latent imagesurfaces, and a resin coating permanently bonded on said core, saidcoating and powder particles having a triboelectric relationship ofopposite polarity, the powder particles thereby being electrostaticallycharged through triboelectric action by mixing with the granular carriermaterial to movably adhere electrostatically to the surface of thecarrier granules and being attractable by an electrostatically-chargedinsulating layer, and the coating of the granular material beingcorrespondingly electrostatically charged to opposite polarity and thusadapted to attract said charged powder particles and to remove them fromuncharged areas of the electrostatic latent image surface when cascadedthereacross.

11. In an electrographic process wherein an electrostatic latent imageis developed to yield an electrostatically adhering image ofelectrostatically-attractable material, the improvement comprisingdeveloping the image by cascading thereacross a dry mixture of loosemovable particles of electrostatically-attractable powder and separategranular carrier material, the granular material being composed ofloose, freely movable particles each of which includes a carborundumcore having a specific gravity higher than the specific gravity of thepowder particles, whereby it does not adhere to electrostatic latentimage surfaces, and a resin coating permanently bonded on said core,said coating and powder particles having a triboelectri'c relationshipof opposite polarity, the powder particles thereby beingelectrostatically charged through triboelectric action by mixing withthe granular carrier material to movably adhere electrostatically to thesurface of the carrier granules and being attractable by anelectrostatically-charged insulating layer, and the coating of thegranular material being correspondingly electrostatically charged toopposite polarity and thus adapted to attract said charged powderparticles and to remove them from uncharged areas of the electrostaticlatent image surface when cascaded thereacross.

12. In an electrophotographic process, the steps of which compriseimposing an electrostatic charge 011 the photoconductive insulatingsurface of an electrophotographic plate havin a photoconductiveinsulating layer on a conductive backing, exposing the charged surfaceto a light image to yield an electrostatic latent image and developingthe electrostatic latent image, the improvement comprising developingthe image by cascading thereacross a dry mixture of loose movableparticles of electrostatically-attractable powder and separate granularcarrier material, the granular material being composed of loose, freelymovable particles each of which includes a core having a specificgravity higher than the specific gravity of the powder particles,whereby it does not adhere to electrostatic latent image surfaces, and aresin coating permanently bonded on said core, said coating and powderparticles having a triboelectric relationship of opposite polarity, thepowder particles thereby being electrostatically charged throughtriboelectric action by mix ing with the granular carrier material tomovably adhere electrostatically to the surface of the carrier granulesand being attractable by an electrostatically-charged insulating layer,and the coating of the granular material being correspondinglyelectrostatically charged to opposite polarity and thus adapted toattract said charged powder particles and to remove them from unchargedareas of the electrostatic latent image surface when cascadedthereacross.

13. A developer for electrostatic latent images comprising a mixture ofloose movable particles of electrostatically attractable powder andseparate granular carrier material, the granular material being composedof loose, freely movable particles each of which includes a core havinga specific gravity and particle size grossly higher than the specificgravity and particle size of the powder particles and a coatingpermanently bonded on said core and having a triboelectric relationshipof opposite polarity to the powder, the powder material being mcvablyand electro statically secured on the surface of said coated granularparticles,

LEWIS E. WALKUP.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 389,552 Dean Sept. 18, 18881,901,325 Novotny Mar. 14, 1933 2,192,241 Robijns Mar. 5, 1940 2,216,728Benner et al Oct. 8, 1940 2,297,691 Carlson 1 Oct. 6, 1942 2,345,941Lehman Apr, 4, 1944 2,440,584 Heltzer et a1. Apr. 27, 1948 2,484,782Copley Oct. 11, 1949

1. A DEVELOPER FOR ELECTROSTATIC LATENT IMAGES COMPRISING A DRY MIXTUREOF LOOSE MOVEABLE PARTICLES OF ELECTROSTATICALLY-ATTRACTABLE POWDER ANDSEPARATE GRANULAR CARRIER MATERIAL, THE GRANULAR MATERIAL BEING COMPOSEDOF LOOSE, FREELY MOVABLE PARTICLES EACH OF WHICH INCLUDES A CORE HAVINGA SPECIFIC GRAVITY HIGHER THAN THE SPECIFIC GRAVITY OF THE POWDERPARTICLES, WHEREBY IT DOES NOT ADHERE TO ELECTROSTATIC LATENT IMAGESURFACES, AND A COATING PERMANENTLY BONDED ON SAID CORE, SAID COATINGAND POWDER PARTICLES HAVING A TRIBOELECTRIC RELATIONSHIP OF OPPOSITEPOLARITY, THE POWDER PARTICLES THEREBY BEING ELECTROSTATICALLY CHARGEDTHROUGH TRIBOELECTRIC ACTION BY MIXING WITH THE GRANULAR CARRIERMATERIAL TO MOVABLY ADHERE ELECTROSTATICALLY TO THE SURFACE OF THECARRIER GRANULES AND BEING ATTRACTABLE BY AN ELECTROSTATICALLYCHARGEDINSULATING LAYER, AND THE COATING OF THE GRANULAR MATERIAL BEINGCORRESPONDINGLY ELECTROSTATICALLY CHARGED TO OPPOSITE POLARITY AND THUSADAPTED TO ATTRACT SAID CHARGED POWDER PARTICLES AND TO REMOVE THEM FROMUNCHARGED AREAS OF THE ELECTROSTATIC LATENT IMAGE SURFACE WHEN CASCADEDTHEREACROSS.